After initial debate, the utility of masks during the Covid-19 pandemic seems widely accepted now. The dominant scientific opinion says masks are very useful, and even relatively simple home-made masks can offer a great degree of protection against the novel coronavirus. In the last few days, several new studies have reinforced this advice with fresh evidence. These studies say the spread can be contained significantly if a large proportion of population begins to use these masks.
Impact of masks, quantified
In one study, researchers from universities in Arizona, Harvard and Sydney have, using mathematical models for population in New York, shown that if 70% of people wore an effective professional mask every time they ventured outdoors, the pandemic could be eliminated from the city. The same result could be achieved in the entire US, if at least 80% of the population regularly used masks.
Even low-quality home-made masks could lead to significant reduction in the spread of the disease, though other interventions would also be required in that case to achieve elimination, the study said.
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“Using face-masks in public (including low-efficacy cloth masks) is very useful in minimising community transmission and burden of COVID-19, provided their coverage level is high. The masks coverage needed to eliminate COVID-19 decreases if the masks-based intervention is combined with strict social distancing strategy,” the researchers have said in their study.
The study also found that up to 45% of the deaths projected in New York over the next two months could be prevented if 80% of the people started using some sort of mask.
“It will be another 12 to 18 months until mass vaccination or herd immunity finally becomes a reality. In the meanwhile, we need to start respecting the mask, change our behaviour and start getting used to this new face accessory on an immediate basis,” said Dr Sundeep Salvi, vice-president of the Indian Chest Society and member of several task forces and committees appointed by central and Maharashtra governments to help tackle the pandemic.
Dr Salvi said the fact that even home-made masks have been found to be quite effective, everyone should start using it. “We now seem to have a solution that is simple, readily available, can be made at home, and is cheap and reusable. Masks, however, need to be worn properly, with a tight fit, and for all the time you are out, otherwise they would not offer any protection,” he said.
More masks, shorter lockdown
Another study, actually a review of available scientific literature, said that for preventing community transmission of the disease, home-made masks were adequate, even if these were about three times less effective than professional surgical masks in blocking transmission of smaller particles.
It said mask usage by a large proportion of the population could help in reducing the lockdown period as well. “When used in conjunction with widespread testing, contact tracing, quarantining of anyone that may be infected, hand washing and physical distancing, face masks are a valuable tool to reduce community transmission,” lead author Jeremy Howard said in an email response.
But he warned that use of masks must not lead to people ignoring physical distancing rules. “We don’t know exactly what the risk reduction (due to masks) is. It is important that people with symptoms stay home, because masks don’t work as well with coughing as with speaking. In general, the further away you are, the safer you are, and adding a mask makes you safer too,” Howard said.
“I would expect the lockdown period to be shorter when masks are universally worn,” he said, warning that if people stop wearing masks, the probability of a “second wave” in winter was “greatly increased”.
Dr Jagmeet Singh, professor of cardiology at Harvard Medical School, said the big value of masks was in the fact that it offered two-way protection. “When people step out of their homes, they should consider others as possibly infected, and themselves as possible contagion. If they wear a mask, there is a two-way protection. They prevent the possibility of infecting others, and also protect themselves.”
Keeping droplets out
In another study, Indian researchers from government and private institutions simulated the aerodynamic flow of particles from the mouth during coughing/sneezing (or speaking loudly) to show how masks could help in blocking airborne transmission of the virus.
“Without a mask, a turbulent jet forms (during the time of coughing or sneezing), and droplets with a broad size distribution are ejected. Large droplets (greater than about 125 microns in diameter) fall to the ground within about 2 metres, while turbulent clouds transport a mist of small aerosolized droplets over significant distances (approximately 5 metres). A loosely fitted simple cotton cloth mask qualitatively changes the propagation of the high velocity jet, and largely eliminates the turbulent cloud downstream of the mask. The spread of the ejecta is also changed, with large droplets trapped at mask surface,” the study said.
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This study was carried out by Guruswamy Kumaraswamy of IIT Bombay, Pankaj Doshi from Pfizer, and Prem Andrade and his colleagues at Pune-based Ansys Software. The study found that while large droplets coming from the mouth were trapped by the mask, smaller ones get transported to muc shorter distances, less than 30 cm, as compared to about 2 m in the absence of a mask.
Within one minute of sneezing by a person who had not worn a mask, approximately 37% of the potential viral load in the ejecta was found deposited on the floor, within 2 metres of the person, while the remaining 63% remained suspended in the air, between 2 metres and 5 metres from the individual. However, when a mask was won, about 70% of virus-laden droplets were deposited on the mask, while those that escaped could potentially take the virus no farther than 1.5 metres, the study found.
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“Virus particles stay suspended within 1.5 m of the person, but this suspended concentration falls off sharply after that distance,” the study said, while concluding that the results suggested that airborne transmission from infected persons could be greatly reduced by wearing a simple cotton mask and maintaining a “strict physical distancing of two metres”.
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